Mechanically alloyed powder feedstock

ABSTRACT

Disclosed herein are embodiments of mechanically alloyed powder feedstock and methods for spheroidizing them using microwave plasma processing. The spheroidized powder can be used in metal injection molding processes, hot isostatic processing, and additive manufacturing. In some embodiments, mechanical milling, such as ball milling, can be used to prepare high entropy alloys for microwave plasma processing.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/656,118 entitled “MECHANICALLY ALLOYED POWDER FEEDSTOCK”, filed onMar. 23, 2022, which is a continuation of U.S. patent application Ser.No. 16/861,594 entitled “MECHANICALLY ALLOYED POWDER FEEDSTOCK”, filedon Apr. 29, 2020, which claims the benefit to U.S. Provisional PatentApplication No. 62/840,607 entitled “MECHANICALLY ALLOYED POWDERFEEDSTOCK”, filed on Apr. 30, 2019, the contents of which is herebyincorporated by reference in its entireties.

BACKGROUND Field

The present disclosure is generally directed in some embodiments towardsproducing metal spherical or spheroidal powder products that includeproperties achieved by mechanical alloying.

Description of the Related Art

Metal powders are being used industrially for certain applications.Recently there is an increased interest in metal powders for use inadditive manufacturing. Metal alloy powders are generally manufacturedby various atomizing techniques—water atomizing, gas atomizing, orthermochemical methods. The morphology of powders produced can depend onthe method of manufacture of the powders. Further, differentmorphologies can be suitable for different consolidation methods or usesof powders. For example, additive manufacturing (AM), especiallylaser-based AM systems such as powder bed fusion, may benefit fromspherical powders due to their excellent flowability, spreadability, andpacking density.

SUMMARY

Disclosed herein are embodiments of a method for manufacturing aspheroidized powder from a mechanically-alloyed feedstock, the methodcomprising preparing a mechanically-alloyed powder feedstock bymechanically milling at least five elemental powders to mechanicallyalloy the at least five elemental powders, introducing themechanically-alloyed powder feedstock into a microwave plasma torch, aplasma plume of the microwave plasma torch, and/or an exhaust of themicrowave plasma torch, and at least partially melting and spheroidizingthe mechanically-alloyed powder feedstock within the microwave plasmatorch, the plasma plume of the microwave plasma torch, and/or theexhaust of the microwave plasma torch to form spheroidized powder.

Also disclosed herein are embodiments of a method for manufacturing aspheroidized powder from a mechanically alloyed feedstock, the methodcomprising preparing a mechanically-alloyed powder feedstock bymechanically milling one or more precursors to form a high entropyalloy, introducing the mechanically-alloyed powder feedstock into amicrowave plasma torch, a plasma plume of the microwave plasma torch,and/or an exhaust of the microwave plasma torch, and at least partiallymelting and spheroidizing the mechanically-alloyed powder feedstockwithin the microwave plasma torch, the plasma plume of the microwaveplasma torch, and/or the exhaust of the microwave plasma torch to formspheroidized powder.

Further disclosed herein are embodiments of a method for manufacturing aspheroidized powder from a mechanically-alloyed feedstock, the methodcomprising introducing a mechanically-alloyed powder feedstock into amicrowave plasma torch, a plasma plume of the microwave plasma torch,and/or an exhaust of the microwave plasma torch, wherein themechanically-alloyed powder feedstock is prepared by mechanicallymilling at least five elemental powders to mechanically alloy the atleast five elemental powders, and melting and spheroidizing themechanically-alloyed powder feedstock within the microwave plasma torch,the plasma plume of the microwave plasma torch, and/or the exhaust ofthe microwave plasma torch to form spheroidized powder.

In some embodiments, the spheroidized powder can be melted andspheroidized for use in metal injection molding processes. In someembodiments, the spheroidized powder can be melted and spheroidized foruse in hot isostatic processing. In some embodiments, the spheroidizedpowder can be melted and spheroidized for use in additive manufacturing.

In some embodiments, the mechanically-alloyed powder feedstock can bemechanically milled by ball milling. In some embodiments, the meltingthe mechanically-alloyed powder feedstock can be performed in less than1 second. In some embodiments, the melting the mechanically-alloyedpowder feedstock can be performed in less than 500 milliseconds.

In some embodiments, the mechanically-alloyed powder feedstock cancomprise TiZrNbTaFe. In some embodiments, the mechanically-alloyedpowder feedstock can comprise AlFeVSi. In some embodiments, themechanically-alloyed powder feedstock can comprise FeCoNiCrTi. In someembodiments, the mechanically-alloyed powder feedstock can compriseFeCoNiCrAl. In some embodiments, the mechanically-alloyed powderfeedstock can comprise FeCoNiCrCu. In some embodiments, themechanically-alloyed powder feedstock can have a microstructure, andwherein the spheroidized powder maintains the microstructure.

A spheroidized powder formed from the method of embodiments of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a transition of an arbitrary feedstock powder withtime.

FIG. 2 illustrates an XRD spectra of powders pre and post microwaveplasma processing.

FIG. 3 illustrates an example embodiment of a method of producingpowders according to the present disclosure.

FIG. 4 illustrates an embodiment of a microwave plasma torch that can beused in the production of powders, according to embodiments of thepresent disclosure.

FIGS. 5A-5B illustrate embodiments of a microwave plasma torch that canbe used in the production of powders, according to a side feeding hopperembodiment of the present disclosure.

FIG. 6 illustrates an embodiment of a mechanical alloying process.

DETAILED DESCRIPTION

Disclosed herein are embodiments of methods, devices, and assemblies forutilizing mechanically alloyed materials (such as powders) as feedstock,in particular for microwave plasma processing and powders and productsproduced from the same. It has been extremely difficult to prepare suchpowders from the mechanically alloyed feedstock, an unexpectedproperties have been achieved based on embodiments of this disclosure.

In some embodiments, materials can be milled together to form a desiredcomposition of particles of a powder, thereby creating mechanicallymilled alloys. Other methods of alloying can be used as well, and thedisclosure is not limited to mechanical milling.

In some embodiments the mechanically milled alloys can be high entropyalloys (HEAs) or can be complex concentrated alloys (CCAs), or can bemodified alloys from existing alloys. HEAs are alloys that primarilycontain 5 or more elements in equi-atomic or non equi-atomic percent.The powder, or other components, can then be used as a feedstock (suchas a powder feedstock) for a microwave plasma process to form a finalspheroidized powder, which can then be used in different processes, suchas additive manufacturing processes.

There is a need to develop novel alloys, such as high entropy alloys(HEA) that yield superior properties when processed with additivemanufacturing methods.

Further, with the advent of additive manufacturing (AM), there is everincreasing need to develop novel alloys that could be processed with AMand could push the envelope of the properties obtained by conventionalor existing alloys.

In some embodiments, HEAs may be alloys that are formed by mixing equalor relatively large proportions of a relatively large number ofelements. In some embodiments, the number of elements within a HEA maybe 3 or more, 4 or more, 5 or more, or 6 or more, 7 or more, 8 or more.In some embodiments, the relative proportions by atomic percentage maybe equal or close to equal. In some embodiments HEAs may be alloys withhigh entropy of mixing, e.g., greater than 1.67R (or greater than about1.67R), such as described in JOM, by Z. Li and D, Raabe, 2017, DOES:10.1007/s11837-017-2540-2, hereby incorporated by reference.

HEAs may have advantageous properties, or combinations of properties,such as high elevated temperature strength, high temperature oxidationresistance, high corrosion resistance and high strength to weight ratioas compared with conventional alloys in use. Due to limited solubilityof elements in each other, most compositions of HEAs, especiallynon-equi atomic HEAs, are difficult or impossible to manufacture bytraditional methods such as arc melting and induction melting. Further,the vast differences in the melting points of the alloying elements inHEAs limit their processing by conventional methods.

Such elements could be alloyed in solid state by mechanical alloyingtechniques, such as where the elemental powders, pre-alloyed powders, ormaster alloy powders are ball milled until a homogeneous alloy isformed. In ball milling, the alloys are mechanically forced to combineinto an alloy. This alloying can then be homogenized with milling time.The homogenization of the alloy is often monitored by x-ray diffraction(XRD), where the initial individual elemental peaks of the alloyingelements gradually disappear, and new peaks of alloyed phase or phasesappear.

With proper ball mill parameters, such as, for example, ball-to-metalratio, rotation speed, and/or ball size, different processes can occurduring the alloying. For example, the resulting powder may haveundergone agglomeration, mechanical alloying, mixing, blending, ormilling. Some or all of which may occur during the process.

The resulting powder, however, is of irregular and flake like morphologylimiting further processing/consolidation techniques such as sparkplasma sintering. Embodiments of this disclosure describe manufacturingof spherical HEA powders processed by mechanical alloying and treatedwith microwave plasma spheroidization. Spherical powders then could beused for a range of industrial powder consolidation processes such asAdditive Manufacturing, Metal Injection Molding, Hot IsostaticProcessing and Powder Forging

Mechanical alloying is a solid-state powder metallurgy process whereelemental or pre-alloyed powder particles are milled with a high energyball mill. Powder particles during this process are subjected torepeated cold welding, fracturing and re-welding. Transfer of mechanicalenergy to the powder particles introduces strain into powder bygenerating dislocations, which act as fast diffusion paths. FIG. 6illustrates an example of such a method. As shown, the elemental powders(left) can be mechanically milled (middle) to produce a feedstock(right).

Further, diffusion distances are reduced due to grain refinement. Thus,an alloy can be manufactured by this process with different phases anddifferent microstructure than that of the base powders. The actualmilling time can vary depending on the feed material and alloy. Forexample, greater than 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 hours (or about1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about9, or about 10 hours). In some embodiments, the milling can last lessthan 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 hours (or about 1, about 2, about3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10hours). In some embodiments, the milling can continue until a partial orcomplete homogenization is attained, such as by monitoring XRD patternsand following the disappearance of the individual elemental peaks.

Advantageously, mechanical alloying may increase the homogenization ofthe particles because the elements are mechanically forced into eachother reducing the diffusion paths between the alloying elements. Thishomogenization also can be enhanced with increased milling time.

Microwave assisted plasma technology can provide for a continuous andsustainable plasma plume with the temperatures reaching on the order of6000K. By adjusting the plasma plume characteristics, such as plumelength and plume density, it is possible to spheroidize and homogenizemechanically alloyed highly irregular or flaky HEA ormechanically-alloyed powders. Further, by adjusting where the feedstockenters the plasma plume, plasma afterglow, or plasma exhaust of themicrowave plasma torch may be used to adjust the temperature thefeedstock is subjected to.

Irregular or flaky powders may limit the processing method to sparkplasma sintering and thus it can be advantageous to spheroidize them formore expanded use across the powder consolidation methods. For example,HIP may benefit from a tap density of the powders to be more than ˜60%of the theoretical density of the alloy in order to achieve full densityafter HIP. Other powder processing methods may benefit from highflowability and/or spreadability of the powder, such as during additivemanufacturing. Irregular and flaky powders have poor flow propertiesmaking then difficult or impossible to process. Thus, microwave plasmaprocessing may transform irregular and flaky powders into spheroidalpowder which may be used for various manufacturing processes.

Due to less residence time in a microwave plasma process, estimated tobe up to few hundred milliseconds, at high temperatures, the powders arepartially melted, which will increase the homogenization of themechanically alloyed powders.

Accelerated processing through microwave plasma processing ofmechanically alloyed particles with heat increases diffusion of thealloying elements into the bulk of the particle, hence increasinghomogeneity. After plasma processing, the spherical HEA powders then canbe processed with various industrial powder consolidation methods suchas, but not limited to, additive manufacturing (AM), metal injectionmolding (MIM), powder forging and hot isostatic pressing (HIP) bringingHEA to mainstream industrial processing.

After feedstock is created from mechanical alloying, the feedstockincludes a certain material composition. The set of process parametersfor microwave plasma processing may be selected based on the materialcomposition. The process parameters may be tailored to allow for varyinghomogeneous alloying and/or spheroidization.

This set of process parameters may include microwave power, plasma gasflows, gas types, plasma plume length, plasma plume diameter, plasma jetvelocity, exhaust chamber pressure, quench gases, exhaust gas velocity,feedstock velocity vis-à-vis plasma jet velocity, feed gas flow, andfeedstock feed-rates, or a combination thereof. This set of processparameters may further include the portion of the plasma, plasma plume,and/or plasma exhaust the feedstock enters into. For example, thefeedstock may be fed in an area of the plasma exhaust that is cooler ifa cooler temperature is desired.

As disclosed herein, melting can include fully melting, partiallymelting, or melting a surface of a particular feedstock.

Feedstock

The feedstock for the microwave plasma processing can be developed bymechanical alloying. Advantageously, mechanical alloying may developalloys which are otherwise difficult or impossible to manufacture byother alloying methods such as arc melting and induction melting. Theunique alloys that can be formed with mechanical alloying include HEAswhich, on laboratory scale have demonstrated unique properties overconventional alloys.

In mechanical alloying, the feedstock can be milled mechanically toachieve homogenization, which can be measured/monitored using XRDtechniques. As the time for mechanical alloying increases, differentpeaks appear on the XRD spectra indicating the formation of alloyedphases. The milling is continued until a stable XRD spectra is obtained,the stable XRD spectra being a spectra which does not change withincreased milling time, thereby indicating a chemically stable alloy.

The resultant powder is highly irregular and flaky due to intensivemechanical milling. For example, an irregular powder can be particleshaving an irregular or angular morphology, such as in water atomizedpowders. On the other hand, flaky powder may have relatively largeaspect ratios and are thin, having very low apparent density and packingdensity, which makes them difficult to flow, spread, and process. Bothirregular and flaky powders are unsuitable for industrial powderconsolidation methods.

However, the resultant powder from mechanical milling has beendemonstrated to be an ideal feedstock for microwave plasma processing.Microwave plasma processing can spheroidize the machined powder which isin irregular or flaky form. FIG. 1 depicts the transition of an examplefeedstock powder with time during the milling process. Illustrated areXRD scans performed on powder that has been mechanically milled for 1hour, 4 hours, 8 hours, and 17 hours. As illustrated, as time increases,several peaks in the XRD scans attenuate or substantially disappear.Further, new peaks are enhanced or appear indicating the formation orincrease of alloyed phases.

HEAs due to their extraordinary properties are of interest to severalapplications. For example, for medical implants TiZrNbTaFe HEAs haveshown much improved corrosion resistance compared to Ti-6Al-4V alloyscurrently being used. AlFeVSi alloys may have high strength and highthermal stability making them of interest to aerospace industry bypotential structural weight reduction. Similarly FeCoNiCrTi orFeCoNiCrAl HEAs have been shown to achieve extraordinary tensileproperties at room temperature making them attractive for manyindustrial applications. In some embodiments, FeCoCrNiCu HEAs can beused.

The mechanically alloyed powder when spheroidized with microwave plasmaprocessing yields highly spherical powder. This spherical powder thencan be used as feedstock material for various industrial consolidationmethods like additive manufacturing, metal injection molding, powderforging and hot isostatic pressing. Advantageously, the microstructure(or nanostructure) of the mechanically milled powders can be maintainedthroughout the processing, such as after the plasma processing.

FIG. 2 shows the XRD spectra of an example powder (having an examplecomposition including 25Fe-17Co-17Cr-17Ni-16Cu before and aftermicrowave plasma processing spheroidization. Other example compositionsinclude Fe-25, Ni-19, Cr-13, Co-0.45, Ti-2.5, Mo-2.4, Nb-0.4, Cu-0.2,Re. The line 202 illustrates an XRD plot of a powder feedstock after 17hours of mechanical alloying but before microwave plasma processing. Theline 204 illustrates an XRD plot of the powder feedstock after microwaveplasma processing.

As shown, the alloy is more homogenized after the spheroidizationprocess. Homogenizing refers to forming an alloy from the startingindividual elemental powders. This can be seen from the XRD spectrumwhere individual peaks representing elements disappear and alloy peaksappear. After spheroidization the alloy peaks are more defined,eliminating remaining background peaks indicating enhancedhomogenization of mechanically alloyed powder. Thus, the microwaveplasma processing not only spheroidizes the powder feedstock but furtherhomogenizes the feedstock.

With proper optimization, the milling time for mechanical alloying canbe reduced because homogenizing can be accomplished using microwaveplasma processing spheroidization. Without being limited to a singletheory, since milling produces refined grains, mechanical alloyinggreatly reduces diffusion distances within the powder. Thus, aftermechanical alloying, during microwave plasma processing, diffusion canoccur rapidly at high temperatures thereby enhancing the homogenizationof the alloy produced by mechanical alloying. Thus, microwave plasmaprocessing can create similar homogenization as long periods of millingtime for mechanical alloying. A milling time may be shortened when thefeedstock is microwave plasma processed.

Mechanical alloying could also be used for alloys other than HEAs. Anyexisting alloy could be manufactured by mechanical alloying for example,stainless steels such as stainless steel type 316 and 17-4, or Ni baseInconels such as 718, 625, 738 etc. Embodiments of the disclosure can beeffectively and economically used to develop new alloys or modifyexisting alloys to be used in emerging consolidation techniques such asAdditive Manufacturing

Mechanical alloying is a solid state process. So technically any alloycould be manufactured by mechanical alloying. However, for conventionalalloys or the alloys that can be manufactured in liquid state such asmelting, these processes are much faster and economical than mechanicalalloying. Hence they are rarely used for such alloys. Nevertheless,mechanical alloying may be used to also produce alloys that can bemanufactured in liquid state such as melting.

Spheroidization

In some embodiments, the final particles achieved by the plasmaprocessing can be spherical or spheroidal, terms which can be usedinterchangeably. Advantageously, by using the critical and specificdisclosure relevant to each of the different feedstocks disclosed, allof the feedstocks can be transformed into the spherical powders.

Embodiments of the present disclosure are directed to producingparticles that are substantially spherical or spheroidal or haveundergone significant spheroidization. In some embodiments, spherical,spheroidal or spheroidized particles refer to particles having asphericity greater than a certain threshold. Particle sphericity can becalculated by calculating the surface area of a sphere A_(s,ideal) witha volume matching that of the particle, V using the following equation:

${r_{ideal} = {\text{?}\sqrt{\frac{3V}{4\pi}}}}{A_{s,{ideal}} = {4\pi r_{ideal}^{2}}}$?indicates text missing or illegible when filed

and then comparing that idealized surface area with the measured surfacearea of the particle, A_(s,actual):

${Sphericity} = {\frac{A_{s,{ideal}}}{A_{s,{actual}}}.}$

In some embodiments, particles can have a sphericity of greater than0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or 0.99 (or greater thanabout 0.5, about 0.6, about 0.7, about 0.75, about 0.8, about 0.8, about0.91, about 0.95, or about 0.99). In some embodiments, particles canhave a sphericity of 0.75 or greater or 0.91 or greater (or about 0.75or greater or about 0.91 or greater). In some embodiments, particles canhave a sphericity of less than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91,0.95, or 0.99 (or less than about 0.5, about 0.6, about 0.7, about 0.75,about 0.8, about 0.8, about 0.91, about 0.95, or about 0.99). In someembodiments, a particle is considered to be spherical, spheroidal orspheroidized if it has a sphericity at or above any of theaforementioned sphericity values, and in some preferred embodiments, aparticle is considered to be spherical if its sphericity is at or about0.75 or greater or at or about 0.91 or greater.

In some embodiments, a median sphericity of all particles within a givenpowder can be greater than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or0.99 (or greater than about 0.5, about 0.6, about 0.7, about 0.75, about0.8, about 0.8, about 0.91, about 0.95, or about 0.99). In someembodiments, a median sphericity of all particles within a given powdercan be less than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or 0.99 (orless than about 0.5, about 0.6, about 0.7, about 0.75, about 0.8, about0.8, about 0.91, about 0.95, or about 0.99). In some embodiments, apowder is considered to be spheroidized if all or a threshold percentage(as described by any of the fractions below) of the particles measuredfor the given powder have a median sphericity greater than or equal toany of the aforementioned sphericity values, and in some preferredembodiments, a powder is considered to be spheroidized if all or athreshold percentage of the particles have a median sphericity at orabout 0.75 or greater or at or about 0.91 or greater.

In some embodiments, the fraction of particles within a powder that canbe above a given sphericity threshold, such as described above, can begreater than 50%, 60%, 70%, 80%, 90%, 95%, or 99% (or greater than about50%, about 60%, about 70%, about 80%, about 90%, about 95%, or about99%). In some embodiments, the fraction of particles within a powderthat can be above a given sphericity threshold, such as described above,can be less than 50%, 60%, 70%, 80%, 90%, 95%, or 99% (or less thanabout 50%, about 60%, about 70%, about 80%, about 90%, about 95%, orabout 99%).

Particle size distribution and sphericity may be determined by anysuitable known technique such as by SEM, optical microscopy, dynamiclight scattering, laser diffraction, manual measurement of dimensionsusing an image analysis software, for example from about 15-30 measuresper image over at least three images of the same material section orsample, and any other techniques.

Microwave Plasma Processing

The process parameters can be optimized to obtain maximumspheroidization depending on the powder initial condition. For eachfeedstock powder characteristic, process parameters can be optimized fora particular outcome. U.S. Pat. Pub. No. 2018/0297122, U.S. Pat. Nos.8,748,785, and 9,932,673 disclose certain processing techniques that canbe used in the disclosed process, specifically for microwave plasmaprocessing. Accordingly, U.S. Pat. Pub. No. 2018/0297122, U.S. Pat. Nos.8,748,785, and 9,932,673 are incorporated by reference in its entiretyand the techniques describes should be considered to be applicable tothe feedstock described herein.

One aspect of the present disclosure involves a process ofspheroidization of metals and metal alloys using a microwave generatedplasma. The powder feedstock is entrained in inert and/or reducingand/or oxidizing gas environment and injected into the microwave plasmaenvironment. Upon injection into a hot plasma, the feedstock isspheroidized and released into a chamber filled with an inert gas anddirected into hermetically sealed drums where is it stored. This processcan be carried out at atmospheric pressure, in a partial vacuum, or at aslightly higher pressure than atmospheric pressure. In alternativeembodiments, the process can be carried out in a low, medium, or highvacuum environment. The process can run continuously and the drums arereplaced as they fill up with spheroidized metal or metal alloyparticles.

The rate of cooling of the spheroidized metal and metal alloys can becontrolled to strategically influence the microstructure of the powder.By controlling the process parameters such as cooling gas flow rate,residence time, cooling gas composition etc., microstructure of themetal and metal alloys can be controlled. The precise cooling ratesrequired to form these structures is largely a function of the type andquantity of the alloying elements within the material.

The rate of cooling, especially when combined with the consistent anduniform heating capabilities of a microwave plasma plume, allow forcontrol over the final microstructure. As a result, the above methodscan be applied to processing metal (e.g., mechanical alloying and/orHEA) feedstock.

Cooling processing parameters include, but are not limited to, coolinggas flow rate, residence time of the spheroidized particles in the hotzone, and the composition or make of the cooling gas. For example, thecooling rate or quenching rate of the particles can be increased byincreasing the rate of flow of the cooling gas. The faster the coolinggas is flowed past the spheroidized particles exiting the plasma, thehigher the quenching rate-thereby allowing certain desiredmicrostructures to be locked-in. Residence time of the particles withinthe hot zone of the plasma can also be adjusted to provide control overthe resulting microstructure. That is, the length of time the particlesare exposed to the plasma determines the extent of melting of theparticle (i.e., surface of the particle melted as compared to the innermost portion or core of the particle).

Consequently, the extent of melting effects the extent of cooling neededfor solidification and thus it is a cooling process parameter.Microstructural changes can be incorporated throughout the entireparticle or just a portion thereof depending upon the extent of particlemelting. Residence time can be adjusted by adjusting such operatingvariables of particle injection rate and flow rate (and conditions, suchas laminar flow or turbulent flow) within the hot zone. Equipmentchanges can also be used to adjust residence time. For example,residence time can be adjusted by changing the cross-sectional area ofthe hot zone.

Another cooling processing parameter that can be varied or controlled isthe composition of the cooling gas. Certain cooling gases are morethermally conductive than others. For example helium is considered to bea highly thermally conductive gas. The higher the thermal conductivityof the cooling gas, the faster the spheroidized particles can becooled/quenched. By controlling the composition of the cooling gas(e.g., controlling the quantity or ratio of high thermally conductivegasses to lesser thermally conductive gases) the cooling rate can becontrolled.

As is known in metallurgy, the microstructure of a metal is determinedby the composition of the metal and heating and cooling/quenching of thematerial. In the present technology, by selecting (or knowing) thecomposition of the feedstock material, and then exposing the feedstockto a plasma that has the uniform temperature profile and control thereover as provided by the microwave plasma torch, followed by selectingand controlling the cooling parameters control over the microstructureof the spheroidized metallic particle is achieved. In addition, thephase of the metallic material depends upon the compositions of the feedstock material (e.g., purity, composition of alloying elements, etc.) aswell thermal processing.

In one exemplary embodiment, inert gas is continually purged surroundinga powdered metal feed to remove oxygen within a powder-feed hopper. Acontinuous volume of powder feed is then entrained within an inert gasand fed into the microwave generated plasma for dehydrogenation or forcomposition/maintaining purity of the spheroidized particles. In oneexample, the microwave generated plasma may be generated using amicrowave plasma torch, as described in U.S. Patent Publication No. US2013/0270261, and/or U.S. Pat. Nos. 8,748,785, 9,023,259, 9,206,085,9,242,224, and 10,477,665, each of which is hereby incorporated byreference in its entirety.

In some embodiments, the particles are exposed to a uniform temperatureprofile at between 4,000 and 8,000 K within the microwave generatedplasma. In some embodiments, the particles are exposed to a uniformtemperature profile at between 3,000 and 8,000 K within the microwavegenerated plasma. Within the plasma torch, the powder particles arerapidly heated and melted. Liquid convection accelerates H₂ diffusionthroughout the melted particle, continuously bringing hydrogen (H₂) tothe surface of the liquid metal hydride where it leaves the particle,reducing the time each particle is required to be within the processenvironment relative to solid-state processes. As the particles withinthe process are entrained within an inert gas, such as argon, generallycontact between particles is minimal, greatly reducing the occurrence ofparticle agglomeration. The need for post-process sifting is thusgreatly reduced or eliminated, and the resulting particle sizedistribution could be practically the same as the particle sizedistribution of the input feed materials. In exemplary embodiments, theparticle size distribution of the feed materials is maintained in theend products.

Within the plasma, the melted metals are inherently spheroidized due toliquid surface tension. As the microwave generated plasma exhibits asubstantially uniform temperature profile, more than 90% spheroidizationof particles could be achieved (e.g., 91%, 93%, 95%, 97%, 99%, 100%).After exiting the plasma, the particles are cooled before enteringcollection bins. When the collection bins fill, they can be removed andreplaced with an empty bin as needed without stopping the process.

FIG. 3 is a flow chart illustrating an exemplary method (250) forproducing spherical powders, according to an embodiment of the presentdisclosure. In this embodiment, the process (250) begins by introducinga feed material into a plasma torch (255). In some embodiments, theplasma torch is a microwave generated plasma torch or an RF plasmatorch. Within the plasma torch, the feed materials are exposed to aplasma causing the materials to melt, as described above (260). Themelted materials are spheroidized by surface tension, as discussed above(260 b). After exiting the plasma, the products cool and solidify,locking in the spherical shape and are then collected (265).

In some embodiments, the environment and/or sealing requirements of thebins are carefully controlled. That is, to prevent contamination orpotential oxidation of the powders, the environment and or seals of thebins are tailored to the application. In one embodiment, the bins areunder a vacuum. In one embodiment, the bins are hermetically sealedafter being filled with powder generated in accordance with the presenttechnology. In one embodiment, the bins are back filled with an inertgas, such as, for example argon. Because of the continuous nature of theprocess, once a bin is filled, it can be removed and replaced with anempty bin as needed without stopping the plasma process.

The methods and processes in accordance with the disclosure can be usedto make powders, such as spherical powders.

In some embodiments, the processing discussed herein, such as themicrowave plasma processing, can be controlled to prevent and/orminimize certain elements for escaping the feedstock during the melt,which can maintain the desired composition/microstructure.

FIG. 4 illustrates an exemplary microwave plasma torch that can be usedin the production of powders, according to embodiments of the presentdisclosure. As discussed above, feed materials 9, 10 can be introducedinto a microwave plasma torch 3, which sustains a microwave generatedplasma 11. In one example embodiment, an entrainment gas flow and asheath flow (downward arrows) may be injected through inlets 5 to createflow conditions within the plasma torch prior to ignition of the plasma11 via microwave radiation source 1.

In some embodiments, the entrainment flow and sheath flow are bothaxis-symmetric and laminar, while in other embodiments the gas flows areswirling. The feed materials 9 are introduced axially into the microwaveplasma torch, where they are entrained by a gas flow that directs thematerials toward the plasma. As discussed above, the gas flows canconsist of a noble gas column of the periodic table, such as helium,neon, argon, etc. Within the microwave generated plasma, the feedmaterials are melted in order to spheroidize the materials. Inlets 5 canbe used to introduce process gases to entrain and accelerate particles9, 10 along axis 12 towards plasma 11. First, particles 9 areaccelerated by entrainment using a core laminar gas flow (upper set ofarrows) created through an annular gap within the plasma torch. A secondlaminar flow (lower set of arrows) can be created through a secondannular gap to provide laminar sheathing for the inside wall ofdielectric torch 3 to protect it from melting due to heat radiation fromplasma 11. In exemplary embodiments, the laminar flows direct particles9, 10 toward the plasma 11 along a path as close as possible to axis 12,exposing them to a substantially uniform temperature within the plasma.

In some embodiments, suitable flow conditions are present to keepparticles 10 from reaching the inner wall of the plasma torch 3 whereplasma attachment could take place. Particles 9, 10 are guided by thegas flows towards microwave plasma 11 were each undergoes homogeneousthermal treatment. Various parameters of the microwave generated plasma,as well as particle parameters, may be adjusted in order to achievedesired results. These parameters may include microwave power, feedmaterial size, feed material insertion rate, gas flow rates, plasmatemperature, residence time and cooling rates. In some embodiments, thecooling or quenching rate is not less than 10⁺³ degrees C./sec uponexiting plasma 11. As discussed above, in this particular embodiment,the gas flows are laminar; however, in alternative embodiments, swirlflows or turbulent flows may be used to direct the feed materials towardthe plasma.

FIGS. 5A-B illustrates an exemplary microwave plasma torch that includesa side feeding hopper rather than the top feeding hopper shown in theembodiment of FIG. 4 , thus allowing for downstream feeding. Thus, inthis implementation the feedstock is injected after the microwave plasmatorch applicator for processing in the “plume” or “exhaust” of themicrowave plasma torch. Thus, the plasma of the microwave plasma torchis engaged at the exit end of the plasma torch to allow downstreamfeeding of the feedstock, as opposed to the top-feeding (or upstreamfeeding) discussed with respect to FIG. 4 . This downstream feeding canadvantageously extend the lifetime of the torch as the hot zone ispreserved indefinitely from any material deposits on the walls of thehot zone liner. Furthermore, it allows engaging the plasma plumedownstream at temperature suitable for optimal melting of powdersthrough precise targeting of temperature level and residence time. Forexample, there is the ability to dial the length of the plume usingmicrowave powder, gas flows, and pressure in the quenching vessel thatcontains the plasma plume.

Generally, the downstream spheroidization method can utilize two mainhardware configurations to establish a stable plasma plume which are:annular torch, such as described in U.S. Pat. Pub. No. 2018/0297122, orswirl torches described in U.S. Pat. Nos. 8,748,785 B2 and 9,932,673 B2.Both FIG. 5A and FIG. 5B show embodiments of a method that can beimplemented with either an annular torch or a swirl torch. A feed systemclose-coupled with the plasma plume at the exit of the plasma torch isused to feed powder axisymmetrically to preserve process homogeneity.

Other feeding configurations may include one or several individualfeeding nozzles surrounding the plasma plume. The feedstock powder canenter the plasma at a point from any direction and can be fed in fromany direction, 360° around the plasma, into the point within the plasma.The feedstock powder can enter the plasma at a specific position alongthe length of the plasma plume where a specific temperature has beenmeasured and a residence time estimated for sufficient melting of theparticles. The melted particles exit the plasma into a sealed chamberwhere they are quenched then collected.

The feed materials 314 can be introduced into a microwave plasma torch302. A hopper 306 can be used to store the feed material 314 beforefeeding the feed material 314 into the microwave plasma torch 302,plume, or exhaust. The feed material 314 can be injected at any angle tothe longitudinal direction of the plasma torch 302. 5, 10, 15, 20, 25,30, 35, 40, 45, 50, or 55 degrees. In some embodiments, the feedstockcan be injected an angle of greater than 5, 10, 15, 20, 25, 30, 35, 40,45, 50, or 55 degrees. In some embodiments, the feedstock can beinjected an angle of less than 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or55 degrees. In alternative embodiments, the feedstock can be injectedalong the longitudinal axis of the plasma torch.

The microwave radiation can be brought into the plasma torch through awaveguide 304. The feed material 314 is fed into a plasma chamber 310and is placed into contact with the plasma generated by the plasma torch302. When in contact with the plasma, plasma plume, or plasma exhaust,the feed material melts. While still in the plasma chamber 310, the feedmaterial 314 cools and solidifies before being collected into acontainer 312. Alternatively, the feed material 314 can exit the plasmachamber 310 while still in a melted phase and cool and solidify outsidethe plasma chamber. In some embodiments, a quenching chamber may beused, which may or may not use positive pressure. While describedseparately from FIG. 4 , the embodiments of FIGS. 5A-5B are understoodto use similar features and conditions to the embodiment of FIG. 4 .

In some embodiments, implementation of the downstream injection methodmay use a downstream swirl, extended spheroidization, or quenching. Adownstream swirl refers to an additional swirl component that can beintroduced downstream from the plasma torch to keep the powder from thewalls of the tube. An extended spheroidization refers to an extendedplasma chamber to give the powder longer residence time. In someimplementations, it may not use a downstream swirl, extendedspheroidization, or quenching. In some embodiments, it may use one of adownstream swirl, extended spheroidization, or quenching. In someembodiments, it may use two of a downstream swirl, extendedspheroidization, or quenching.

Injection of powder from below may result in the reduction orelimination of plasma-tube coating in the microwave region. When thecoating becomes too substantial, the microwave energy is shielded fromentering the plasma hot zone and the plasma coupling is reduced. Attimes, the plasma may even extinguish and become unstable. Decrease ofplasma intensity means decreases in spheroidization level of the powder.Thus, by feeding feedstock below the microwave region and engaging theplasma plume at the exit of the plasma torch, coating in this region iseliminated and the microwave powder to plasma coupling remains constantthrough the process allowing adequate spheroidization.

Thus, advantageously the downstream approach may allow for the method torun for long durations as the coating issue is reduced. Further, thedownstream approach allows for the ability to inject more powder asthere is no need to minimize coating.

From the foregoing description, it will be appreciated that inventiveprocessing methods for mechanically alloyed and/or HEA powder aredisclosed. While several components, techniques and aspects have beendescribed with a certain degree of particularity, it is manifest thatmany changes can be made in the specific designs, constructions andmethodology herein above described without departing from the spirit andscope of this disclosure.

Certain features that are described in this disclosure in the context ofseparate implementations can also be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation can also be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations, one or more features from a claimed combination can, insome cases, be excised from the combination, and the combination may beclaimed as any subcombination or variation of any subcombination.

Moreover, while methods may be depicted in the drawings or described inthe specification in a particular order, such methods need not beperformed in the particular order shown or in sequential order, and thatall methods need not be performed, to achieve desirable results. Othermethods that are not depicted or described can be incorporated in theexample methods and processes. For example, one or more additionalmethods can be performed before, after, simultaneously, or between anyof the described methods. Further, the methods may be rearranged orreordered in other implementations. Also, the separation of varioussystem components in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described components and systems cangenerally be integrated together in a single product or packaged intomultiple products. Additionally, other implementations are within thescope of this disclosure.

Conditional language, such as “can,” “could,” “might,” or “may,” unlessspecifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include or do not include, certain features, elements,and/or steps. Thus, such conditional language is not generally intendedto imply that features, elements, and/or steps are in any way requiredfor one or more embodiments.

Conjunctive language such as the phrase “at least one of X, Y, and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y, or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require the presence of atleast one of X, at least one of Y, and at least one of Z.

Language of degree used herein, such as the terms “approximately,”“about,” “generally,” and “substantially” as used herein represent avalue, amount, or characteristic close to the stated value, amount, orcharacteristic that still performs a desired function or achieves adesired result. For example, the terms “approximately”, “about”,“generally,” and “substantially” may refer to an amount that is withinless than or equal to 10% of, within less than or equal to 5% of, withinless than or equal to 1% of, within less than or equal to 0.1% of, andwithin less than or equal to 0.01% of the stated amount. If the statedamount is 0 (e.g., none, having no), the above recited ranges can bespecific ranges, and not within a particular % of the value. Forexample, within less than or equal to 10 wt./vol. % of, within less thanor equal to 5 wt./vol. % of, within less than or equal to 1 wt./vol. %of, within less than or equal to 0.1 wt./vol. % of, and within less thanor equal to 0.01 wt./vol. % of the stated amount.

The disclosure herein of any particular feature, aspect, method,property, characteristic, quality, attribute, element, or the like inconnection with various embodiments can be used in all other embodimentsset forth herein. Additionally, it will be recognized that any methodsdescribed herein may be practiced using any device suitable forperforming the recited steps.

While a number of embodiments and variations thereof have been describedin detail, other modifications and methods of using the same will beapparent to those of skill in the art. Accordingly, it should beunderstood that various applications, modifications, materials, andsubstitutions can be made of equivalents without departing from theunique and inventive disclosure herein or the scope of the claims.

1. (canceled)
 2. A spheroidized powder prepared by a method comprising:introducing a mechanically alloyed feedstock into a microwave plasmatorch, a plasma plume of the microwave plasma torch, and/or an exhaustof the microwave plasma torch, the mechanically alloyed feedstockprepared by milling a plurality of elemental powders or pre-alloyedpowders; and contacting the mechanically alloyed feedstock with a plasmawithin the microwave plasma torch, the plasma plume of the microwaveplasma torch, and/or the exhaust of the microwave plasma torch to formspheroidized powder, wherein the spheroidized powder comprises a highentropy alloy (HEA), and wherein the mechanically alloyed feedstockcomprises TiZrNbTaFe, AlFeVSi, FeCoNiCrTi, FeCoNiCrAl, or FeCoNiCrCu. 3.The spheroidized powder of claim 2, wherein the mechanically alloyedfeedstock is milled by ball milling.
 4. The spheroidized powder of claim2, wherein the mechanically alloyed feedstock comprises amicrostructure, and wherein the spheroidized powder maintains themicrostructure.
 5. The spheroidized powder of claim 2, furthercomprising varying one or more of the following parameters afterintroducing the mechanically alloyed feedstock into the microwave plasmatorch, the plasma plume of the microwave plasma torch, and/or theexhaust of the microwave plasma torch: microwave power, plasma gas flow,gas type, plasma plume length, plasma plume diameter, plasma jetvelocity, exhaust chamber pressure, quench gas type, exhaust gasvelocity, feedstock velocity, feed gas flow, and feedstock feed rate. 6.The spheroidized powder of claim 2, wherein the plurality of elementalpowders or pre-alloyed powders are mechanically milled for between about1 hour and about 17 hours.
 7. The spheroidized powder of claim 2,wherein the mechanically alloyed feedstock comprises a high entropyalloy.
 8. The spheroidized powder of claim 2, wherein the mechanicallyalloyed feedstock comprises a non-equiatomic high entropy alloy.
 9. Thespheroidized powder of claim 2, wherein the spheroidized powdercomprises a sphericity greater than 0.5.
 10. The spheroidized powder ofclaim 2, wherein the spheroidized powder comprises a sphericity greaterthan 0.75.
 11. The spheroidized powder of claim 2, wherein thespheroidized powder comprises a sphericity greater than 0.9.
 12. Thespheroidized powder of claim 2, wherein the spheroidized powdercomprises a sphericity greater than 0.99.
 13. A spheroidized alloypowder prepared by a method comprising: introducing a mechanicallyalloyed feedstock into a microwave plasma torch, a plasma plume of themicrowave plasma torch, and/or an exhaust of the microwave plasma torch,the mechanically alloyed feedstock prepared by milling one or morepowders to form an alloy; and contacting the mechanically alloyedfeedstock with a plasma within the microwave plasma torch, the plasmaplume of the microwave plasma torch, and/or the exhaust of the microwaveplasma torch to form spheroidized powder, wherein the spheroidizedpowder comprises an entropy of mixing of greater than about 1.67R, andwherein the mechanically alloyed feedstock comprises TiZrNbTaFe,AlFeVSi, FeCoNiCrTi, FeCoNiCrAl, or FeCoNiCrCu.
 14. The spheroidizedalloy powder of claim 13, wherein the mechanically alloyed feedstock ismechanically milled by ball milling.
 15. The spheroidized alloy powderof claim 13, wherein the alloy comprises a non-equiatomic high entropyalloy.
 16. The spheroidized alloy powder of claim 13, further comprisingvarying one or more of the following parameters after introducing themechanically alloyed feedstock into the microwave plasma torch, theplasma plume of the microwave plasma torch, and/or the exhaust of themicrowave plasma torch: microwave power, plasma gas flow, gas type,plasma plume length, plasma plume diameter, plasma jet velocity, exhaustchamber pressure, quench gas type, exhaust gas velocity, feedstockvelocity, feed gas flow, and feedstock feed rate.
 17. The spheroidizedalloy powder of claim 13, wherein the one or more powders aremechanically milled for between about 1 hour and about 17 hours.
 18. Thespheroidized alloy powder of claim 13, wherein the spheroidized powdercomprises a sphericity greater than 0.5.
 19. The spheroidized alloypowder of claim 13, wherein the spheroidized powder comprises asphericity greater than 0.75.
 20. The spheroidized alloy powder of claim13, wherein the spheroidized powder comprises a sphericity greater than0.9.
 21. The spheroidized alloy powder of claim 13, wherein thespheroidized powder comprises a sphericity greater than 0.99.